function res = CrankNicholson_diffusionConvection_solve(u,N,x_max,k)
D1 = Mat1(N,x_max);
D2 = Mat2(N,x_max);
tmp = eye(N)-0.5*k*D1-0.5*k*D2; 
res = u(1:N)/tmp;
res = [res,res(1)];